This is the ValueSet that contains all the codes in AllergyIntolerance Certainty ValueSet (http://hl7.org/fhir/ValueSet/reaction-event-certainty) and AllergyIntolerance Certainty ValueSet (http://hl7.org/fhir/ValueSet/reaction-event-certainty). E.g. what you have to deal with if you get resources containing codes in either of them